| Description |
Over the Intermountain West, cyclones and cold fronts can bring about dramatic sensible weather changes that impact the rapidly growing population of the region, yet the basic mechanisms contributing to their intensification and evolution are not well understood. This dissertation investigates these mechanisms using a multi-faceted approach that includes observational analysis, real-data model simulations, and idealized model simulations. Chapter 2 presents an observational analysis of the 15 Apr 2002 Tax Day Storm, which featured the strongest cyclone and cold front to pass through Salt Lake City, Utah in recent history. In particular, we establish the role of a newly identified feature, the Great Basin Confluence Zone (GBCZ), in cyclone and frontal evolution. This region of contraction (confluent deformation and divergence) extends downstream from the Sierra Nevada and is initially nonfrontal, but becomes the locus for frontogenesis and cyclogenesis. Chapter 3 uses real-data and idealized modeling studies to examine the role of the Sierra Nevada in Intermountain cold front evolution. Using model simulations of another strong case of Intermountain frontogenesis from 25 Mar 2006 with and without the Sierra Nevada, we show that the range produces a leeward warm anomaly, increasing the cross-front potential temperature contrast, and also enhances contraction along the front. Idealized baroclinic wave simulations in which we vary the initial cyclone position are used to show how the influence of the Sierra Nevada varies for differing synoptic patterns and frontal orientations. This work advances our understanding of the mechanisms important to cyclone and frontal evolution over mountainous terrain and should contribute to improved analysis and forecasting of cyclones and fronts over the Intermountain West. |
